A framework coupling farm typology and biophysical modelling to assess the impact of vegetable crop-based systems on soil carbon stocks. Application in the Caribbean

Agricultural land devoted to vegetable crops in the Caribbean has strongly increased during the past twenty years, which raises major concerns regarding a reduction in soil organic carbon (SOC) stocks because of low C inputs and high SOC outputs from these cropping systems. The aim of this study was to assess the impact of farming practices on SOC stocks at the farm type level. We designed a framework which encompasses a farm typology describing the diversity of farm practices applied to vegetable crops and a model of SOC dynamics to estimate the impact of these practices on SOC stocks. The study was carried out in the Guadeloupe archipelago, which offers a good representation of the variability of Caribbean agriculture, in a context of transition from traditional sugarcane and banana monocultures for export to a more diversified agriculture including vegetable crops. A farm typology was developed from a survey of 71 farmers concerning their socio-economic characteristics and farming practices. The MorGwanik model of SOC dynamics was then used to assess the impact of farming practices on SOC at the farm type level, and to interpret the observed SOC changes. Five farm types were identified varying from traditional export agriculture with low diversification to monoculture of vegetable crops based on compost application and reduced soil tillage. The observed and simulated results indicated that systems with a fallow/vegetables cycle ratio>2 and the monoculture of vegetables including compost applications at ≥10Mgha−1yr−1 presented C sequestration corresponding to SOC increases of 10% and 3% of the initial stock, respectively. The monoculture of vegetables with a compost rate<10Mgha−1yr−1 and systems including vegetables in rotation with export crops and a short fallow cycle presented a reduction in SOC that ranged from 10% to 18%. Pedoclimatic conditions had a lower impact on SOC changes. Similar socio-economic profiles of farmers were observed for farm types including very different cropping systems. The model well described SOC changes for each farm type and offered valuable insights about the factors affecting SOC losses and C sequestration. The framework proposed in this study was helpful to identify improved managements that can maintain or increase SOC stocks under tropical conditions.